Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-03-20
2003-11-25
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S510000
Reexamination Certificate
active
06653392
ABSTRACT:
The present invention relates to an adhesive system comprising an etherified amino resin, a polymer prepared from one or more ethylenically unsaturated monomers, a curing agent and a polyvinyl alcohol. The present invention also relates to the use of the adhesive system for gluing wood-based products and to a hardener composition for use in amino resin based gluing systems. Furthermore, the invention relates to a method of application of the adhesive system.
Adhesives systems suitable for use in wood-based constructions for outdoor use are generally based on formaldehyde resins, such as phenol-resorcinol-formaldehyde (PRF), phenol-formaldehyde (PF) and melamine-urea-formaldehyde (MUF). The major disadvantages of these adhesive systems are their long curing time at room temperature (~20° C.) and week bonding performance at temperatures below 20° C. Typical pressing times for these systems are in the range of 5 to 24 hours at 20° C. In addition to that, an after curing time, especially for melamine based resins, of several days is needed before the beams can be transported to the customers. These factors, of course, hamper seriously the productivity in, for example, laminated beam industries.
Furthermore, it is also known that amino resins, such as urea-formaldehyde (UF) resin, can be combined with dispersions of polymers of vinylic, acrylic, or butadiene-styrene type, in order to obtain improved bonding performance. Adhesives based merely on dispersions of polymers, like polyvinyl acetate, are not at all suitable for use in load bearing constructions. They do not meet the standards for, e.g., laminated beams. This is mainly due to their thermoplastic properties imparting creep in the construction and a poor durability.
EP 0 501 174 B1 discloses a hardening composition for urea-formaldehyde glues containing an aqueous emulsion of a polyvinyl acetate comprising post-crosslinking groups, an ammonium salt and urea. However, this hardening composition is not suitable for adhesive systems that have to be cured at room temperature, or at lower temperatures.
Thus, technical solutions are still sought for the need to find adhesive systems, which are fast curing even at room temperature or at lower temperatures and provide constructions with strong glue joints that meet the required standards for the end use products.
Accordingly, the present invention provides an adhesive system; a hardener composition suitable for use in amino resin based adhesive systems and a method of application of the adhesive system, by which the above-mentioned problems can be overcome.
The adhesive system according to the invention is defined in the appended claims. It comprises (a) an etherified amino resin, (b) a polymer prepared from one or more ethylenically unsaturated monomers, (c) a curing agent, and (d) a polyvinyl alcohol.
The etherified amino resin used in the adhesive system according to the invention, as the resin component, can be any etherified amino resin, such as etherified urea-formaldehyde, etherified melamine-urea-formaldehyde, etherified melamine-formaldehyde, or etherified melamine-urea-phenol-formaldehyde resin. Preferred etherified amino resins are etherified melamine-urea-formaldehyde and etherified melamine-formaldehyde and most preferred is etherified melamine-formaldehyde.
The term “etherified amino resin”, as used herein refers to an amino resin that has been modified by reaction with an alcohol, such as methanol, ethanol or butanol. The degree of etherification can be defined by
13
C NMR according to, e.g., the following formula:
Degree of etherification
=
RNCH
2
O—
CH
3
RNHCH
2
O—
CH
3
+
CH
2
OH
×
100
%
Suitably the etherified amino resin has a degree of etherification of 4-95% preferably 10-75% and most preferably 30-60%.
The resin component in the adhesive system may be comprised of a mixture of an etherified and a non-etherified amino resin. Suitable non-etherified amino resins include urea-formaldehyde, melamine-urea-formaldehyde, melamine-formaldehyde and melamine-urea-phenol-formaldehyde.
The amount of the etherified amino resin in the resin component is suitably 4≧weight %, preferably ≧50.0 weight %, and most preferably ≧90.0 weight %, based on the solids of the resin component.
The total amount of the resin component in the adhesive system is suitably 10-90 weight %, preferably 40-85 weight % and most preferably 50-80 weight %, based on the solids of the adhesive system.
The polymer according to the invention is suitably a homopolymer or copolymer prepared from one or more ethylenically unsaturated monomers. Examples of suitable ethylenically unsaturated monomers are vinylic monomers, such as vinyl esters, e.g., vinyl acetate, vinyl propionate, vinyl butyrate and comonomers thereof with, e.g., ethylene; alkyl esters of acrylic and methacrylic acid such as methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, etc.; butadiene-styrene and derivates thereof, such as carboxylated butadiene-styrene; substituted or unsubstituted mono- and dialkyl esters of alpha, beta-unsaturated dicarboxylic acids such as the substituted and unsubstituted mono- and dibutyl, mono- and diethyl maleate esters as well as the corresponding fumarates, itaconates and citronates; alpha beta-unsaturated carboxylic acids such as crotonic, acrylic and methacrylic acids and mixtures thereof. Polymers based on vinyl acetate are preferred. Preferably the polymer is prepared from at least 50 weight % vinyl acetate, based on the total weight of the monomers.
According to a preferred embodiment of the invention the polymer comprises post-crosslinking groups. The post-crosslinking groups can be incorporated into the polymer by copolymerising one or more ethylenically unsaturated monomers with at least one monomer comprising at least one post-crosslinking group. Suitable post-crosslinking groups include N-alkylol, N-alkoxymethyl, carboxylate and glycidyl groups.
By post-crosslinking monomer is herein meant a monomer having a first reactive functional group that renders the monomer copolymerisable with ethylenically unsaturated comonomer(s) and a second functional group that does not enter into the copolymerisation reaction during formation of the polymer, but provides a reactive site on the copolymer that may subsequently be reacted under, for example, acidic conditions, with another reactive site on the copolymer and/or the amino resin to crosslink the copolymer and/or the amino resin.
Suitable post-crosslinking monomers include, N-alkylol acrylamides, e.g., N-methylol acrylamide, N-ethanol acrylamide, N-propanol acrylamide, N-methylol methacrylamide, N-ethanol methacrylamide, N-propanol methacrylamide, N-methylol maleamide, N-methylol maleamic acid, N-methylol maleamic acid esters; the N-alkylol amides of the vinyl aromatic acids, such as N-methylol-p-vinylbenzamide and the like; also N-(alkoxymethyl) acrylates and methacrylates, where the alkyl group has from 1-8 carbon atoms, such as N-(methoxymethyl) acrylamide, N-(butoxymethyl) acrylamide, N-(methoxymethyl) methacrylamide, N-(butoxymethyl) allyl carbamate and N-(methoxymethyl) allyl carbamate, and mixtures of these monomers with allyl carbamate, acrylamide or methacrylamide; and also triallyl cyanurate. Preferably N-methylol acrylamide, or N-(butoxymethyl) acrylamide is used.
The polymer is suitably prepared from 0.1-10 weight % and preferably 0.2-6 weight % post-crosslinking monomer, based on the total weight of the monomers.
In a preferred embodiment the copolymer is based on vinyl acetate and N-methylol acrylamide.
The amount of the polymer in the adhesive system is suitably 5-60 weight %, preferably 10-50 weight % and most preferably 15-30 weight %, based on the solids of the adhesive system.
Mixtures of polymers containing post-crosslinking groups and polymers without post-crosslinking groups may also be used according to the invention. For example, the polymer may comprise both polyvinyl acetate without post-crosslinking groups and vinyl acetate based polymer containing post-crosslinking
Lindberg Stefan
Nasli-Bakir Benyahia
Akzo Nobel N.V.
Cain Edward J.
Serbin David J.
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